The present invention relates to a disk drive and a control method in the disk drive, aimed at providing improved recording characteristics. In particular, the invention relates to a disk drive and a control method of the disk drive, which is suitable for improvement in overwrite characteristics.
As well known, there are a wide variety of data storage devices which use different types of media such as optical disks and magnetic tapes. Hard disk drives (HDD) have widely used and have been one of the indispensable storage devices for today's computer systems. The use of the HDD has been not limited to computers and has proliferated due to the superior characteristics. The HDDs are now used in moving picture recording/reproducing apparatus, car navigation systems, cellular phones, removable memories for digital cameras and the like.
The HDD comprises a magnetic disk to record data thereon, and a head which performs data writing into and data reading from the magnetic disk. The head has a head element section which is a thin film element, and a slider having the head element section disposed thereon. The head element section has a write element section and a read element section. The write element section converts an electrical signal to a magnetic field according to write data for the magnetic disk, and the read element section converts a magnetic field generated from the magnetic disk to an electrical signal. Typically, the write element section and the read element section are formed on a thin film device in an integration fashion.
In general, the write element section is constituted by using an inductive thin film element. A head amp circuit changes the polarity of a write current which flows in the thin film element based on binary write data. By increasing, at a high speed, a switching frequency for switching the polarity of the write current which flows in the thin film element, it is possible to increase the density of binary data recorded on the disk. Since the thin film element has a coil structure, however, the write current (effective current) flowing in the thin film element is more impeded as the frequency is increased. Thus, a higher power supply voltage is needed to obtain higher recording density in the magnetic disk drive.
To obtain a higher power supply voltage in a drive, an arrangement in which a booster is disposed in a disk drive has been proposed, for example, in Patent Document 1 Japanese Patent Laid-Open No. 2005-78748. According to the technique disclosed in Patent Document 1, a voltage boosted by a booster is supplied only to a write current driver of a head amp circuit. The purposes of the technique are to prevent decrease of the rising speed of a write current, ensure good recording characteristics even for high density recording, and minimize an increase in power consumption, even if a power supply voltage of the disk storage device is low.
The overwrite characteristics are improved by increasing a write current. This can obtain good recording characteristics. Generally, with respect to writing data to the disk in the HDD, previously written data is overwritten with new data. The overwrite characteristics are an important index of the recording characteristics of the HDD. The overwrite characteristics depend on how much the original data that is overwritten is completely erased. That is, the overwrite characteristics are defined as the attenuation rate of a low frequency signal.
The overwrite characteristics may be judged according to whether a signal can properly be read out from the disk after the disk is overwritten with the signal under poor conditions. For example, in the case of a in-plane (horizontal) magnetic recording system, if a signal written to the disk is composed of patterns 1L through 9L, data composed of the longest pattern 9L is first written by a write head. This pattern 9L is read out by a read head. The read head outputs a read signal having a single peak at a low frequency f9L corresponding to the pattern 9L. Then, the pattern L1 is overwritten in a disk area, in which the pattern 9L is written, at a high frequency f2 corresponding to the shortest pattern 1L. The thus written pattern 1L is read out by the read head. This read signal includes a peak at the previous low recording frequency f9L (residual components) as well as a peak at the high frequency f1L.
If the residual components of the previously written data signal are significant, unexpected signal components are included in a read signal, resulting in poor overwrite characteristics. That is, poor overwrite characteristics make it difficult to correctly recognize a read signal, making data rewriting impossible.
In the case of the in-plane magnetic recording system, as the switching frequency for switching the polarity of the write current flowing in the thin film element is increased, solitary waves increasingly interfere with each other. This impedes the effective write current and therefore causes deterioration in the overwrite characteristics. Further, if the write current value is lower than an assumed value due to a variation of the write head itself, the overwrite characteristics deteriorate particularly when data with a short pattern length is written in a high frequency range that is close to the specified operating frequency range of the head amp. The overwrite characteristics can be improved by increasing the write current as described in Patent Document 1.
Further, in the case of the in-plane magnetic recording system, high frequency recording poses a problem that the magnetization of a recording layer on the disk can not be saturated sufficiently due to the reduced effective write current. To avoid this or generate a head recording magnetic field sufficient to saturate the magnetization of the recording layer on the disk, the write current must be increased by using such a technique as described in Japanese Patent Laid-Open No. 2005-78748 (Patent Document 1).
To sufficiently improve the overwrite characteristics or obtain a necessary head recording magnetic field, however, increasing the write current may cause adjacent track interference (ATI). In this case, since the recording magnetic field from the write head acts not only on the target track but also on its adjacent tracks, the recording characteristics may deteriorate.
Embodiments in accordance with the present invention address the above-referenced issues.